Compressor Unit

ABSTRACT

The invention relates to a compressor unit, in particular for underwater operations, comprising a compressor with a rotational axis and an electric motor. Said compressor unit has a housing with an automation unit for control and regulation tasks. The aim of the invention is to improve the co-operation of the automation unit and the compressor unit and in particular to reduce the complexity of the cooling of the automation unit and signal and energy transmission. To achieve this, an additional housing, which contains the automation unit, is attached to the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2007/051474, filed Feb. 15, 2007 and claims the benefitthereof. The International Application claims the benefits of Europeanapplication No. 06006059.7 filed Mar. 24, 2006, both of the applicationsare incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a compressor unit, in particular for underwateroperation, comprising a compressor with a rotation axis and an electricmotor, which compressor unit has a housing which has an inlet and anoutlet for a pumping medium, having an automation unit which is designedsuch that it carries out open-loop and closed-loop control tasks for thecompressor unit.

BACKGROUND OF THE INVENTION

Recent developments in the field of compressor design have also beenconcentrated on undersea arrangements of large compressors which areintended to be used for the pumping of natural gases.

Because of the particular operating conditions, in particular because ofthe greatly restricted accessibility both for maintenance purposes andby means of supply lines, the specialists are confronted with majorrequirements. The relevant environmental regulations forbid any exchangeof substances between the equipment to be installed and the surroundingseawater. Furthermore, seawater is an aggressive medium and extremepressure and temperature conditions can be found at the various depthsin the sea. A further requirement is that the equipment should on theone hand have an extremely long life and on the other hand must bedesigned to be virtually free of maintenance. An additional exacerbatingfactor is not-inconsiderable contamination of the medium to be pumpedwhich in some cases is chemically aggressive.

Compressor units normally require numerous electrical connections fortheir operation, in particular for the power supply and for transmissionof control signals between a higher-level automation unit and thecompressor unit. The higher-level automation units are in this casearranged separately from the compressor unit, at some distance away, onthe one hand in order to achieve a high level of modularity of design,and on the other hand to ensure optimum operating conditions for theelectronics of the automation unit. Particularly when using activemagnetic bearings, numerous signal lines are required between theautomation unit and the compressor unit, and transmit various measuredvalues to the automation unit, and transmit corresponding controlparameters to the magnetic bearings.

The transmission of the power for operation of the compressor unit andof the signals between the compressor unit and the automation unitnecessitates a considerable amount of complexity since the numerouslines must be designed, inter alia, to be disconnectable by means of avery costly plug connection. The cost aspect becomes many times moreimportant when this relates to an installation which is suitable forundersea operation, since the plug connection has to comply withparticular requirements for this purpose.

Furthermore, the automation unit must be provided with a cooling systemby means of which the not-inconsiderable lost power from the components,some of which are in the form of power electronics, must be dissipated.

The document WO-A-2005/003512 has already disclosed a compressor unitfor underwater operation in which the compressor together with anelectric motor is accommodated in a common, gas-tight housing. Anautomation unit, which controls the operation of magnetic bearings, isconnected for signal transmission purposes to these bearings.

SUMMARY OF INVENTION

Against the background of the problems of the prior art, the object ofthe invention is to provide a better interaction between the automationunit and the compressor unit and, in particular, to reduce thecomplexity for cooling the automation unit and of the signal and powertransmission.

A compressor unit is proposed in order to achieve the object accordingto the invention.

The arrangement of an additional housing, in which the automation unitis arranged, on the housing of the compressor unit has, in particular,the advantage that appropriate power supply lines and signal linesbetween the automation unit and the compressor unit need no longer bedesigned to comply with a standard which is suitable for direct contactwith the environmental conditions. In fact, these lines can be designedsuch that they merely satisfy the always reproducible and exactlypredictable operating conditions in the interior of the additionalhousing and of the housing of the compressor unit. Furthermore, nospecial plug connections are required for disconnection of lines betweenthe automation unit and the compressor unit. Surprisingly, it was alsofound that some areas on the housing of the compressor unit satisfy thethermal constraints required for operation of the automation unit,without any additional modification. This major advantage means thatthere is no longer any need for a separate cooling system for theautomation unit. This advantage is particularly evident when theadditional housing for the automation unit is thermally conductivelyfitted to the housing in the area of an intake connecting stub of theinlet such that the power lost from the automation unit is dissipated bymeans of thermal conduction to the housing. Although this advantage isfundamentally relevant for compressor units, it is additionallyimportant in the field of underwater operation since, in this case, theaccessibility to the compressor unit is very greatly restricted and, forthis reason, additional cooling media are available only withdifficulty, if at all. It is virtually impossible to use seawater as acooling medium, because of the aggressive chemical characteristics. Whenpumping natural gas, the lost power can be absorbed without any problemsby the cold pumping medium. However, one problem in this case is theintroduction of the heat into the pumped flow.

Particularly when a compressor unit is of a single-shaft design with amotor and a compressor unit along a single rotation axis, it is normallyin an elongated form thus resulting in a temperature profile in thelongitudinal extent during operation. The temperature in the axial areaof the inlet or of the intake connecting stub is particularlyadvantageous for thermally conductive fitting of the additional housingfor the automation unit. According to the invention, the heat isdissipated from the automation unit by means of thermal conduction inthe area of the intake connecting stub of the housing, and introducedinto the pumping medium flowing through the compressor unit. A personskilled in the art can decide the circumferential position in the axialarea of the intake connecting stub at which the additional housing isfitted, depending on the thermal-conduction conditions between thehousing of the compressor unit and the additional housing.

In this case, the automation unit is expediently connected to componentsof the compressor unit by means of internal signal lines and/or internalpower supply lines. These internal lines can expediently be designed tobe disconnectable by means of a plug connection, such that elements canbe replaced without any problems even during the course of maintenancetasks. The plug connections need be designed only to satisfy the alwaysreproducible and predictable operating conditions in the housinginterior. The components which are connected to the automation unit are,in particular, magnetic bearings for the rotor of the compressor and ofthe motor, and the electric motor. In addition, various temperaturemeasurements and pressure measurements can be provided.

The automation unit is expediently connected to a base station by meansof an external signal line or an external power supply line, or by meansof both.

One advantageous development of the invention provides for theadditional housing to be connected to the housing of the compressor unitby means of welding, which on the one hand ensures good thermalconduction between the housings and on the other hand provides therequired gas-tightness, in particular for underwater operation. In orderto ensure that the components in the additional housing are neverthelessaccessible for maintenance tasks, it is advantageous for the additionalhousing to have an opening which can be closed. This opening which canbe closed can be sealed by means of a conventional seal. For relativelylong underwater operation phases, it is also feasible for thisadditional opening to be sealed by means of a weld seam, which in anycase withstands the adverse operating conditions.

In order to reliably dissipate on the one hand the lost power from theautomation unit and on the other hand that from the operation of thecompressor unit, it is expedient for the compressor unit itself to havea high-performance cooling system. This cooling system may, inparticular during the pumping of natural gas during underwateroperation, be designed such that the pumping medium flows around variouscomponents of the compressor unit, and the lost heat is in this wayemitted to the pumping medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following textusing one specific exemplary embodiment for illustrative purposes, andwith reference to drawings. The embodiment shown should be regarded onlyas being illustrative, as one example of the invention. In the FIGURE:

FIG. 1 shows a longitudinal section through a compressor unit with anautomation unit fitted according to the invention, in the form of aschematic illustration.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a section along a compressor unit 1 according to theinvention which has, as major components, a motor 2 and a compressor 3in a housing 4 which is designed to be gas-tight. The housing 4accommodates the motor 2 and the compressor 3. In the area of thejunction between the motor 2 and the compressor 3, the housing 4 isprovided with an inlet 6 and an outlet 7, with the fluid to becompressed being sucked in through the inlet 6 by means of an intakeconnecting stub 8, and with the compressed fluid flowing out through theoutlet 7.

The compressor unit 1 is arranged vertically during operation, with amotor rotor 15 of the motor 2 being combined via a compressor rotor 9 ofthe compressor 3 to form a common shaft 19, which rotates about a commonvertical rotation axis 60.

The motor rotor 15 is mounted in a first radial bearing 21 at the upperend of the motor rotor 15.

The compressor rotor 9 is mounted in a second radial bearing 22 at alower position.

An axial bearing 25 is therefore provided at the upper end of the motorrotor 15, at the upper end of the common shaft 19. The radial bearings21, 22 and the axial bearing 25 operate electromagnetically, and areeach designed to be encapsulated. The radial bearings 21, 22 in thiscase extend in the circumferential direction around the respectivebearing point of the shaft 19, and in this case are designed to revolvethrough 360° and not to be split.

The compressor 3, which is in the form of a centrifugal compressor, hasthree compressor stages 11 which are each connected by means of anoverflow 33. The pressure differences which result across the compressorstages 11 ensure a thrust on the compressor rotor 9, which istransmitted via a coupling to the motor rotor 15 and is in the oppositedirection to the force produced by the weight of the entire resultantrotor comprising the compressor rotor 9 and the motor rotor 15, suchthat this results in a very high degree of thrust matching during ratedoperation. This allows the axial bearing 25 to be designed to becomparatively smaller than in a horizontal arrangement.

The electromagnetic bearings 21, 22, 25 are cooled to operatingtemperature by means of a cooling system 31, with the cooling system 31providing a tap 32 in an overflow of the compressor 3. A portion of thepumping medium, which is preferably natural gas, is passed from the tap32 by means of pipelines through a filter 35, and is then passed throughtwo separate pipelines to the respective outer bearing points (firstradial bearing 21 and second radial bearing 22 as well as the axialbearing 25). This cooling by means of the cold pumping medium savesadditional supply lines.

The motor rotor 15 is surrounded by a stator 16 which has anencapsulation 39, such that the aggressive pumping medium does notdamage the windings of the stator 16. The encapsulation 39 is in thiscase preferably designed such that it can withstand the full operatingpressure. This is also because a separate stator cooling arrangement 40is provided, which pumps a dedicated cooling medium 41 via a heatexchanger 43 by means of a pump 42. At least the encapsulation 39 isdesigned such that the section which extends between the stator 16 andthe motor rotor 15 admittedly has a thin wall thickness, but is able towithstand the design pressure when the stator cooling arrangement 40 iscompletely filled by means of the cooling medium 41. This avoidsrelatively major eddy current losses in this area, and improves theefficiency of the overall arrangement.

The compressor rotor 9 expediently has a compressor shaft 10 on whichthe individual compressor stages 11 are mounted. This can preferably beachieved by means of a thermal shrink fit. An interlock, for example bymeans of polygons, is likewise possible. Another embodiment provides forthe various compressor stages 11 to be welded to one another, thusresulting in an integral compressor rotor 9.

An additional housing 56 is thermally conductively fitted to the housing4 of the compressor unit 1 by means of a weld seam 58. The additionalhousing 56 has an opening 57 through which the interior of theadditional housing 56 is accessible, and which is closed by means ofscrews 59 and a cover 70. The cover 70 is welded by means of a sealingjoint 63 to the adjacent elements of the additional housing 56 in orderthat the surrounding medium cannot enter during underwater operation. Anautomation unit 51, comprising power electronics 52 and furthercomponents, is located in the interior of the additional housing 56. Theautomation unit 51 is thermally conductively connected to the housing 4of the compressor unit by means of a thermal-conduction element 64, suchthat the lost power that is created is dissipated by means of thermalconduction to the housing 4.

The additional housing 56 is arranged in the axial area 50 of the inlet6, or of the intake connecting stub 8, of the compressor unit such thatthe thermal conditions which prevail there ensure particularly efficientcooling of the automation unit 51. A specific temperature profile occursalong the rotation axis 60 of the compressor unit during operation, andessentially has a low point in the area of the intake connecting stub 8.

The automation unit 51 is connected by means of external signal lines 66and external power supply lines 68 to a station 65 which on the one handcontrols, and on the other hand supplies, the compressor unit 1. Theexternal signal lines 66 and power supply lines 68 are designed suchthat they can be disconnected by means of external plug connections 69.A bushing 53 seals the inlet of the external lines (66, 68) into theadditional housing 56.

The automation unit 51 is connected to components of the compressor unit1 by means of internal signal lines 55 and internal power supply lines67. The components comprise an axial bearing 25, radial bearings 21, 22and the motor 2. In addition, further sensors and components are alsoprovided and are connected to the automation unit 51, although they willnot be explained in any more detail here.

The additional housing is formed from stainless steel, in particular forunderwater operation. The power supply originating from the base station65 is 400 V.

1.-9. (canceled)
 10. A compressor unit for underwater operation,comprising: a rotation axis and an electric motor; a housing with aninlet and an outlet for a pumping medium; an automation unit thatcarries out open-loop and closed-loop control tasks for the compressorunit, wherein an additional housing in which the automation unit isarranged, is arranged on the housing.
 11. The compressor unit as claimedin claim 10, wherein the additional housing is thermally conductivelyfitted to the housing in the area of an intake connecting stub of theinlet such that the power lost from the automation unit is dissipatedvia thermal conduction to the housing.
 12. The compressor unit asclaimed in claim 11, wherein the pumping medium is natural gas, and thecompressor unit is constructed and suitable for underwater operation.13. The compressor unit as claimed in claim 12, wherein the automationunit is connected to components via internal signal lines and/orinternal power supply lines.
 14. The compressor unit as claimed in claim13, wherein the components are magnetic bearings and/or the motor. 15.The compressor unit as claimed in claim 14, wherein the automation unitis connected to a station via external signal lines and/or externalpower supply lines.
 16. The compressor unit as claimed in claim 15,wherein the additional housing is welded to the housing.
 17. Thecompressor unit as claimed in claim 16, wherein the additional housinghas a closeable opening.
 18. The compressor unit as claimed in claim 17,further comprising a cooling system which provides a tap and is designedsuch that the compressor unit is cooled via the pumping medium.